(a) Field of the Invention
This invention relates to an improved method for separating polymer powder from a carrier gas by introducing a mixture of the polymer powder and carrier gas into a cyclone separator and feeding out the thus-separated polymer powder by a rotary feeder from a hopper provided below the cyclone separator.
(b) Description of the Prior Art
It has been widely known to introduce a mixture of a polymer and one or more highly volatile monomers, which mixture has been obtained upon polymerization of the monomers, as a mixed stream of monomer gas and polymer powder into a cyclone separator, to draw the monomer gas from an upper part of the cyclone separator, to draw the polymer powder through a lower part of the cyclone separator into a hopper and then to feed out the polymer powder from the hopper upon separation of the mixture into the polymer and the monomer or monomers (see, for example, Japanese Patent Publication No. 3587/1964 and Japanese Patent Laid-Open No. 90329/1974). It is also routinely practiced to convey polymer powder as its mixture with a carrier gas and then to separate the thus-conveyed mixture in the same manner as that described above. It is also commonly practiced to adjust the amount of a polymer, which is to be discharged out from a hopper, by using a rotary feeder and varying the revolution speed of the rotary feeder.
In an actual production process of polymer powder, the amount of polymer powder to be introduced in a cyclone separator is not always constant but is subject to variations. Moreover, the flowability of the polymer powder changes depending on the molecular weight, composition, etc. of the polymer. When the rotary feeder is driven at a constant revolution speed, the above-mentioned variations may lead to variations in the powder level in the hopper and, in some instances, may result in clogging of the hopper. Reduced flowability of the polymer powder may on the other hand lead to clogging of a polymer powder guide disposed between the cyclone separator and hopper. As a result, the separation of the polymer powder from the carrier gas in the cyclone separator may become no longer feasible. Accordingly, the cyclone separator is usually operated while controlling the revolution speed of the rotary feeder in such a way that the height of the top of the powder in the hopper is maintained at a constant level. This method is however not effective for the possible clogging between the cyclone separator and hopper.